Foamed well cement slurries, additives and methods

ABSTRACT

The present invention provides improved foamed well cement slurries, additives and methods. The foamed well cement slurries are basically comprised of a hydraulic cement, sufficient water to form a pumpable slurry, sufficient gas to form a foam and an effective amount of an additive for foaming the slurry comprised of hydrolyzed keratin.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to foamed well cement slurries, additivesfor foaming the cement slurries and methods of using the slurries.

2. Description of the Prior Art

Hydraulic cement slurries are commonly utilized in subterranean wellcompletion and remedial operations. For example, hydraulic cementslurries are used in primary cementing operations whereby strings ofpipe such as casings and liners are cemented in well bores. Inperforming primary cementing, a hydraulic cement slurry is pumped intothe annular space between the walls of a well bore and the exteriorsurfaces of a pipe string disposed therein. The cement slurry ispermitted to set in the annular space thereby forming an annular sheathof hardened substantially impermeable cement therein. The cement sheathphysically supports and positions the pipe in the well bore and bondsthe exterior surfaces of the pipe to the walls of the well bore wherebythe undesirable migration of fluids between zones or formationspenetrated by the well bore is prevented.

In carrying out primary cementing as well as remedial cementingoperations in well bores, the cement slurries utilized must often belight weight to prevent excessive hydrostatic pressure from beingexerted on subterranean formations penetrated by the well bore. As aresult, a variety of light weight cement slurries have heretofore beendeveloped and used including foamed cement slurries.

In addition to being light weight, a foamed cement slurry containscompressed gas which improves the ability of the slurry to maintainpressure and prevent the flow of formation fluids into and through theslurry during its transition time, i.e., the time during which thecement slurry changes from a true fluid to a hard set mass. Foamedcement slurries are also advantageous because they have low fluid lossproperties.

While foamed cement slurries have included various surfactants known asfoaming and foam stabilizing agents or additives for facilitating thefoaming and stabilizing of cement slurries when a gas is mixedtherewith, the heretofore used foaming and stabilizing additives havenot met complete environmental requirements. That is, when the foamingand stabilizing additives find their way into water in the environment,they do not fully degrade which can result in interference with aquaticlife cycles.

Thus, there are needs for improved foamed well cement slurries, improvedcement slurry foaming and stabilizing additives which degrade completelyin the environment and are totally harmless thereto and improved methodsof utilizing the foamed well cement slurries.

SUMMARY OF THE INVENTION

The present invention provides improved foamed well cement slurries,improved foaming additives for foaming and stabilizing the cementslurries which are totally harmless to the environment and methods ofusing the improved foamed well cement slurries which meet the needsdescribed above and overcome the deficiencies of the prior art. Theimproved foamed cement slurries are basically comprised of a hydrauliccement, sufficient water to form a pumpable slurry, sufficient gas toform a foam and an effective amount of an environment harmless additivefor foaming and stabilizing the slurry comprised of hydrolyzed keratin.

The cement slurry foaming and stabilizing additive which is harmless tothe environment is keratin which has been base hydrolyzed to form aprotein powder. The additive is preferably pre-dissolved in water toform an aqueous solution which is added to the cement slurry along witha gas for foaming the slurry.

The methods of the present invention comprise the steps of forming afoamed cement slurry of the present invention comprised of hydrauliccement, sufficient water to form a pumpable slurry, sufficient gas toform a foam and an effective amount of the above describedenvironmentally safe additive for foaming and stabilizing the cementslurry, placing the foamed cement slurry into a subterranean zone by wayof a well bore penetrating the zone and then allowing the foamed cementslurry to set into a hard impermeable mass therein.

It is, therefore, a general object of the present invention to provideimproved foamed well cement slurries, additives and methods.

Other and further objects, features and advantages of the presentinvention will be readily apparent to those skilled in the art upon areading of the description of preferred embodiments which follows.

DESCRIPTION OF PREFERRED EMBODIMENTS

The improved foamed cement slurries of this invention are useful forperforming a variety of completion and remedial procedures insubterranean formations. The foamed cement slurries are basicallycomprised of a hydraulic cement, sufficient water to form a pumpableslurry, sufficient gas to form a foam and an effective amount of theimproved foaming additive of this invention for foaming and stabilizingthe slurry comprised of hydrolyzed keratin.

A variety of hydraulic cements can be utilized in accordance with thepresent invention including those comprised of calcium, aluminum,silicon, oxygen and/or sulphur which set and harden by reaction withwater. Such hydraulic cements include Portland cements, pozzolanacements, gypsum cements, high aluminum content cements, silica cements,high alkalinity cements and slag cements. The cements can be ofconventional particle sizes or they can be of ultra-fine particle sizes.Portland cements are generally preferred for use in accordance with thisinvention. Portland cements of the types defined and described in APISpecification For Materials And Testing For Well Cements, APISpecification 10, 5^(th) Edition, dated Jul. 1, 1990 of the AmericanPetroleum Institute are particularly suitable. Preferred such APIPortland cements include classes A, B, C, G and H, with API classes Gand H being more preferred and class G being the most preferred.

The water in a foamed cement slurry of this invention can be fresh wateror saltwater. The term “saltwater” is used herein to mean unsaturatedsalt solutions and saturated salt solutions including brines andseawater. The water is present in the cement slurry in an amountsufficient to form a pumpable slurry, generally an amount in the rangeof from about 38% to about 56% by weight of cement in the slurry.

The gas utilized for forming a foamed cement slurry of this inventioncan be air or nitrogen, with nitrogen being preferred. The gas ispresent in an amount sufficient to foam the cement slurry, generally inan amount in the range of from about 10% to about 40% by volume of thecement slurries.

Keratin¹ is the structural protein of epithellal cells in the outermostlayers of skin. Hydrolyzed keratin is manufactured by the basehydrolysis of hoof and horn meal. That is, the hoof and horn meal isheated with lime in an autoclave to produce a hydrolyzed protein. Theamino acid content, i.e., the number of gram molecules of amino acid per1000 grams of protein, is as follows: Lysine-6.2; Histidine-19.7;Arginine-56.9; Aspartic Acid²-51.5; Threonine-55.9; Serine-79.5;Glutamic acid²-99; Proline-58.3; Glycine-78; Alanine-43.8; Halfcystine-105; Valine-46.6; Methionine-4; Isoleucine-29; Leucine-59.9;Tryosine-28.7; Phenylalanine-22.4; Hydroxyproline- 12.2;Hydroxylsine-1.2; Total-863; Average residual weight-117. The protein iscommercially available as a free flowing powder that contains about 85%protein. The non-protein portion of the powder consists of about 0.58%insoluble material with the remainder being soluble non-proteinmaterials primarily made up of calcium sulfate, magnesium sulfate andpotassium sulfate.

The hydrolyzed keratin protein powder is preferably predissolved infresh water in an amount of about 50% by weight of the solution. Inaddition to water for dissolving the hydrolyzed keratin, the additivecan include other components such as one or more freezing and pour pointdepressants to prevent it from freezing during storage or handling incold weather and lower its pour point. Preferably, such depressants areselected from the group of propylene glycol, sodium chloride andmixtures thereof. The depressant or depressants utilized are generallypresent in the additive solution in an amount in the range of from about1% to about 5% by weight of the solution.

The hydrolyzed keratin is preferably included in a foamed cement slurryof this invention in an amount in the range of from about 1% to about 5%by volume of the water in the foamed cement slurry (from about 2% toabout 10% of a 50% by weight solution of the hydrolyzed keratin).

The foamed cement slurries of this invention may be prepared inaccordance with any of the mixing techniques utilized in the art. In onepreferred method, a quantity of water is introduced into a cementblender followed by the hydraulic cement utilized. The mixture isagitated for a sufficient period of time to form a pumpable non-foamedslurry. The slurry is then pumped to the well bore, and the additivesolution of this invention for foaming the slurry followed by the gasutilized are injected into the slurry on the fly. As the slurry and gasflow through the well bore to the location where the resulting foamedcement composition is to be placed, the slurry is foamed. Other liquidadditives utilized, if any, are added to the water prior to when thehydraulic cement is mixed therewith and other dry solids, if any, areadded to the water and cement prior to mixing.

The methods of this invention of cementing a subterranean zonepenetrated by a well bore basically comprise the steps of forming afoamed cement slurry of this invention, pumping the foamed cement slurryinto the subterranean zone to be cemented by way of the well bore andthen allowing the foamed cement slurry to set into a hard impermeablemass therein.

In order to further illustrate the improved cement slurries, additivesand methods of this invention, the following examples are given.

EXAMPLE 1

Test samples of foamed cement slurries of this invention comprised ofPortland Class G cement, fresh water or saltwater and air were prepared.For each test sample, an unfoamed cement slurry was first preparedutilizing a mixing device. Predetermined amounts of the resulting slurrywere then placed in fixed volume blender jars adapted for receiving astacked blade assembly. The additive of this invention for foaming andstabilizing a cement composition was added to some of the test samplesand three prior art additives consisting of mixtures of foaming agentsand foam stabilizers were added to the other samples. The foaming andstabilizing additive of the present invention used in the testsconsisted of a 50% by weight aqueous solution of hydrolyzed keratin.

The first prior art additive designated as “Prior Art Additive A” isdescribed in detail in U.S. Pat. No. 6,063,738 issued to Chatteiji etal. on May 16, 2000 and consisted of 63.3 parts by weight of anethoxylated alcohol ether sulfate surfactant, 31.7 parts by weight ofcocoylamidopropyl betaine surfactant and 5 parts by weight ofcocoylamidopropyl dimethyl amine oxide surfactant. The second prior artadditive designated as “Prior Art Mixture B” is described in detail inU.S. Pat. No. 5,897,699 issued to Chatteiji et al. on Apr. 27, 1999 andconsisted of a mixture of 2 parts by weight of an alpha-olefin sulfonatesurfactant and 1 part by weight of cocoylamidopropyl betaine surfactant.The third prior art additive designated as “Prior Art Mixture C”consisted of a mixture of 2 parts by weight of an ethoxylated alcoholether sulfate surfactant and 1 part by weight of cocoylamidopropylbetaine surfactant. After the addition of the additive of this inventionand the prior art additives to the test samples in the jars, thecontents were mixed at high speed. The high speed mixing by the stackedblade assembly caused each slurry to be foamed with air. The densitiesof the non-foamed cement slurries, the densities of the foamed cementslurries, the quantities of foaming additives combined with the cementslurries in order to obtain stable foams in 10 seconds or less and thequantities of salt (sodium chloride) added to the water used to form thecement slurries are set forth in Table I below.

The foamed test samples were allowed to set for 24 hours at 140° F. andatmospheric pressure after which they were subjected to compressivestrength and thickening time tests conducted in accordance with theprocedures set forth in the API Specification 10 mentioned above. Theresults of the tests are also set forth in Table I below.

TABLE I Foamed Portland Cement Slurries Formed With Various FoamingAdditives Quantity of 50% Maximum Quantity of Unfoamed Foamed FoamingTime Sodium Cement Cement Additive Required to Chloride in 24 HourThickening Surfactant Slurry Slurry Solution Form a Water, % CompressiveTime at Slurry Mixture Density, Density, Used, % by Stable Foam, of wt.of Strength at 140° F., No. Used lb/gal lb/gal vol. of water sec water140° F., psi hr:min  1 Present Invention 15.92 11.2 2.5 10  0 1029 7:00 2 Present Invention 16.07 11.2 2.5 10  5 1276 —  3 Present Invention16.31 11.2 2.5 10 10 1210 —  4 Present Invention 16.7 11.2 2.5 10 181038 —  5 Present Invention 17.62 11.2 2.5 10 37  380 20:00   6 PriorArt Mixture A¹ 15.8 11.2 2 10  0 1103 3:05  7 Prior Art Mixture A¹ 15.9511 2 10  5  900 —  8 Prior Art Mixture A¹ 16.2 11 2 10 10 1220 —  9Prior Art Mixture A¹ 16.59 11.5 2 10 18 1013 — 10 Prior Art Mixture A¹17.51 11.2 2 10 37  625 5:45 11 Prior Art Mixture B² 15.8 11.2 2.5 10  0 505 3:00 12 Prior Art Mixture B² 15.95 11 2.5 10  5  710 — 13 Prior ArtMixture B² 16.2 11 2.5 10 10  725 — 14 Prior Art Mixture B² 16.59 11.52.5 10 18  780 3:15 15 Prior Art Mixture B² 17.51 11.2 2.5 10 37  460 —16 Prior Art Mixture C³ 15.8 11.2 2.5 10  0  759 2:45 17 Prior ArtMixture C³ 15.95 11 2.5 10  5 1328 — 18 Prior Art Mixture C³ 16.2 11 2.510 10 1123 2:45 19 Prior Art Mixture C³ 16.59 11.5 2.5 10 18 1081 3:3020 Prior Art Mixture C³ 17.51 11.2 2.5 10 37  581 6:15 ¹63.3 parts byweight ethoxylated alcohol ether sulfate, 31.7 parts by weightcocoylamidopropyl betaine and 5 parts of weight cocoylamidopropyldimethyl amine oxide ²2 parts by weight alpha-olefin sulfonate and 1part by weight cocoylamidoprpyl betaine ³2 parts by weight ethoxylatedhexanol ether sulfate and 1 part by weight cocoylamidopropyl betaine

From Table I it can be seen that the foaming additive of the presentinvention produced stable foamed cement slurries in 10 seconds or less.It is generally accepted that if a foaming and stabilizing additiverequires more than 10 seconds in the laboratory to generate a stablefoam, the additive is not acceptable in field operations. Further, thecompressive strengths of the set foamed cement slurries utilizing theadditive of the present invention were generally as good or better thanthe compressive strengths of the set foamed cement slurries containingthe prior art additives. Also, the presence of salt in the cement slurrymixing water does not affect the performance of the foaming additive ofthe present invention.

EXAMPLE 2

The procedure described in Example 1 was repeated except that instead ofstandard particle size Portland cement, an ultra-fine particle sizePortland cement was utilized. The ultra-fine particle size cement whichwas used is commercially available from Halliburton Energy Services ofDuncan, Oklahoma under the trade designation “MICRO MATRIX^(™)” and ithas an average particle size of about 7.5 microns. The results of thesetests are given in Table II below.

TABLE II Foamed Ultra-Fine Cement Slurries Foamed With Various FoamingAdditives Quantity of 50% Maximum Quantity of Unfoamed Foamed FoamingTime Sodium Cement Cement Additive Required to Chloride in 24 HourThickening Surfactant Slurry Slurry Solution Form a Water, % CompressiveTime at Slurry Mixture Density, Density, Used, % by Stable Foam, of wt.of Strength at 140° F., No. Used lb/gal lb/gal vol. of water sec water140° F., psi hr:min 21 Present Invention 12.03 10 2.5 10  0 475 1:40 22Present Invention 12.26 10 2.5 10  5 678 — 23 Present Invention 12.58 102.5 10 10 782 — 24 Present Invention 13.09 10 2.5 10 18 631 3:25 25Present Invention 14.32 10 2.5 10 37 423 — 26 Prior Art Mixture A¹ 12.0310 1 10  0 835 1:00 27 Prior Art Mixture A¹ 12.26 10 1 10  5 830 — 28Prior Art Mixture A¹ 12.58 10 1 10 10 820 — 29 Prior Art Mixture A¹13.09 10 1.5 10 18 720 0:50 30 Prior Art Mixture A¹ 14.32 10 2.5 10 37619 — 31 Prior Art Mixture B² 12.03 10 2.5 10  0 467 1:00 32 Prior ArtMixture B² 12.26 10 2.5 10  5 312 — 33 Prior Art Mixture B² 12.58 10 2.510 10 819 — 34 Prior Art Mixture B² 13.09 10 2.5 10 18 634 — 35 PriorArt Mixture B² 14.32 10 2.5 20 37 564 0.45 36 Prior Art Mixture C³ 12.0310 2.5 10  0 795 1:00 37 Prior Art Mixture C³ 12.26 10 2.5 10  5 946 —38 Prior Art Mixture C³ 12.58 10 2.5 10 10 875 0;43 39 Prior Art MixtureC³ 13.09 10 2.5 10 18 852 — 40 Prior Art Mixture C³ 14.32 10 2.5 15 37839 0:48 ¹63.3 parts by weight ethoxylated alcohol ether sulfate, 31.7parts by weight cocoylamidopropyl betaine and 5 parts of weightcocoylamidopropyl dimethyl amine oxide ²2 parts by weight alpha-olefinsulfonate and 1 part by weight cocoylamidoprpyl betaine ³2 parts byweight ethoxylated hexanol ether sulfate and 1 part by weightcocoylamidopropyl betaine

From Table II it can be seen that the surfactant mixture of the presentinvention produced stable foamed cement slurries in 10 seconds or less.In addition, the presence of salt in the cement slurry mixing water doesnot affect the performance of the surfactant mixture of the presentinvention.

EXAMPLE 3

The tests and procedures described in Example 1 above were repeatedexcept that slag cement was substituted for Portland cement. The resultsof these tests are set forth in Table III below.

TABLE III Foamed Slag Cement Slurries Formed With Various FoamingAdditives Quantity of 50% Maximum Quantity of Unfoamed Foamed FoamingTime Sodium Cement Cement Additive Required to Chloride in 24 HourThickening Surfactant Slurry Slurry Solution Form a Water, % CompressiveTime at Slurry Mixture Density, Density, Used, % by Stable Foam, of wt.of Strength at 140° F., No. Used lb/gal lb/gal vol. of water sec water140° F., psi hr:min 41 Present Invention 15.03 12 5 10  0 1239 4:30 42Present Invention 15.18 12 5 10  5 1549 — 43 Present Invention 15.42 125 10 10 1554 — 44 Present Invention 15.8 12 5 10 18 1096 3:25 45 PresentInvention 16.71 12 3 10 37 1008 1:50 46 Prior Art Mixture A¹ 15.03 12 210  0 2250 1:20 47 Prior Art Mixture A¹ 15.18 12 2 10  5 — — 48 PriorArt Mixture A¹ 15.42 12 2 10 10 — — 49 Prior Art Mixture A¹ 15.80 12 210 18 — — 50 Prior Art Mixture A¹ 16.71 12 3.5 10 37 1588 0:40 51 PriorArt Mixture B² 15.03 12 3.5 would not foam 52 Prior Art Mixture B² 15.1812 3.5 would not foam 53 Prior Art Mixture B² 15.42 12 3.5 would notfoam 54 Prior Art Mixture B² 15.80 12 3.5 would not foam 55 Prior ArtMixture B² 16.71 12 3.5 would not foam 56 Prior Art Mixture C³ 15.03 123.5 10  0 1715 1:15 57 Prior Art Mixture C³ 15.18 12 3.5 10  5 2340 — 58Prior Art Mixture C³ 15.42 12 3.5 10 10 1597 — 59 Prior Art Mixture C³15.80 12 3.5 20 18 1692 — 60 Prior Art Mixture C³ 16.71 12 3.5 30 371338 0:37 ¹63.3 parts by weight ethoxylated alcohol ether sulfate, 31.7parts by weight cocoylamidopropyl betaine and 5 parts of weightcocoylamidopropyl dimethyl amine oxide ²2 parts by weight alpha-olefinsulfonate and 1 part by weight cocoylamidoprpyl betaine ³2 parts byweight ethoxylated hexanol ether sulfate and 1 part by weightcocoylamidopropyl betaine

From Table III it can again be seen that the surfactant mixture of thepresent invention produced stable foams in 10 seconds or less.

EXAMPLE 4

The tests and procedures described in Example 1 above were repeatedexcept that the foaming additives were added to a special lowtemperature cement slurry comprised of standard particle size PortlandClass A cement mixed with the ultra-fine particle size Portland cementdescribed in Example 2 above in an amount of 18% ultra-fine cement byweight of the cement mixture, calcium chloride in an amount of 2% byweight of the cement mixture, a dry cement free flow additive present inan amount of 0.055% by weight of the cement mixture and seawater inamounts sufficient to form cement slurries having the densities setforth in Table IV below. The results of the tests are also set forth inTable IV below.

TABLE IV Foamed Low Temperature Cement Slurries With Various SurfactantMixtures Quantity of 50% Maximum Unfoamed Foamed Foaming Time CementCement Additive Required to 24 Hour Thickening Surfactant Slurry SlurrySolution Form a Compressive Time at Slurry Mixture Density, Density,Used, % by Stable Foam, Strength at 65° F., No. Used lb/gal lb/gal vol.of water sec 45° F., psi hr:min 61 Present Invention 15.3 12 2.5 10 7070 62 Prior Art Mixture A¹ 15.24 12 1 10 381 4:00 63 Prior Art Mixture B²15.17 12 1 10 345 2:45 64 Prior Art Mixture C³ 15.17 12 2.25 10 348 4:03¹63.3 parts by weight ethoxylated alcohol ether sulfate, 31.7 parts byweight cocoylamidopropyl betaine and 5 parts of weight cocoylamidopropyldimethyl amine oxide ²2 parts by weight alpha-olefin sulfonate and 1part by weight cocoylamidoprpyl betaine ³2 parts by weight ethoxylatedhexanol ether sulfate and 1 part by weight cocoylamidopropyl betaine

From Table IV it can again be seen that the foaming additive of thepresent invention produces stable foamed cement slurries having goodcompressive strengths at low temperatures.

EXAMPLE 5

A number of the foamed cement slurries formed in accordance with theprocedure set forth in Example 1 were tested for Theological propertiesin accordance with the procedures set forth in the above mentioned APISpecification 10. The results of these tests are set forth in Table Vbelow.

TABLE V Rheological Properties Of Foamed Cement Slurries SurfactantSlurry Mixture Viscosity at Room Temperature, cp No. Used 600 rpm 300rpm 200 rpm 100 rpm 6 rpm 3 rpm  1 Present Invention 116  64 49 24 15 11 5 Present Invention 98 60 46 30 13 11  6 Prior Art Mixture A¹ 118  7563 50 21 14  8 Prior Art Mixture A¹ 90 54 42 35 18 15 13 Prior ArtMixture B² 78 48 36 26 13 12 15 Prior Art Mixture B² 78 50 42 32 17 1416 Prior Art Mixture C³ 150  88 80 68 24 18 21 Present Invention 79 3832 26 17 14 26 Prior Art Mixture A¹ 68 54 48 40 24 20 28 Prior ArtMixture A¹ 75 56 51 40 25 21 33 Prior Art Mixture B² 76 44 35 26 14 1238 Prior Art Mixture C³ 79 53 42 35 20 16 41 Present Invention 70 55 4838 21 16 48 Prior Art Mixture A¹ 69 54 47 38 24 20 58 Prior Art MixtureC³ 68 55 49 40 25 22 ¹63.3 parts by weight ethoxylated alcohol ethersulfate, 31.7 parts by weight cocoylamidopropyl betaine and 5 parts ofweight cocoylamidopropyl dimethyl amine oxide ²2 parts by weightalpha-olefin sulfonate and 1 part by weight cocoylamidoprpyl betaine ³2parts by weight ethoxylated hexanol ether sulfate and 1 part by weightcocoylamidopropyl betaine

From Table V it can be seen that the foamed cement slurries containingthe foaming additive of the present invention have low apparentviscosities which indicates that the placement of such foamed cementslurries in subterranean formations will not result in formationbreakdown due to high pumping pressures exerted thereon.

EXAMPLE 6

Three different test cement slurries were prepared which included thefoaming additive of this invention. The various components and amountsincluded in the cement slurries are set forth in Table VI below.

TABLE VI Cement Slurry Components And Amounts Finely High GroundAmorphous Temperature Crystalline Silica, Anti-Settling Set FreshFoaming Silica, % by wt. Agent¹, Retarder², Water, Additive, SlurrySlurry Hydraulic % by wt. of % by wt. % by wt. % by wt. % by wt.Density, No. Cement of cement cement of cement of cement of cement ofwater lb/gal 1 Portland Class H 30 15 0.4 1.2 52.3 2.0³ 16.11 2 PortlandClass H 30  5 — 0.8 52.6 2.5⁴ 16 3 Portland Class H 30 — — 0.8 51.3 2.5⁴16 ¹Hydroxypropyl guar substituted with 0.6-0.8 moles of propyleneoxide. ²A non-dispersing retarder comprised of a mixture Kraftlignosulfonate, xylos and lignosulfonates produced by the bisulfitemethod. ³Two parts by weight ethoxylated hexanol ether sulfate and onepart by weight cocoylamidopropyl betaine - U.S. Pat. No. 5,897,699⁴Foaming additive of the present invention, i.e., hydrolyzed keratin ina 50% by weight fresh water solution.

Test samples of the three test cement slurries described above weretested for thickening time in accordance with the procedure set forth inthe above mentioned API Specification 10. The results of these tests aregiven in Table VII below.

Additional test samples of the three cement slurries described abovewere foamed with nitrogen to the densities given in Table VII below at250° F. and 1000 psi. The foamed samples were then cured at 318° F. and1000 psi for 24 hours. The cured samples were then cut into top, middleand bottom sections and the densities of the samples were determined.The results of these tests are also given in Table VII below.

TABLE VII Set Foamed Cement Slurry Settling Tests Set Foamed CementFoamed Section Density, lb/gal² Thickening Slurry Total Slurry Time¹,Density, Density No. hrs:min lb/gal Top Middle Bottom Variation 1 4:0712.1  11.98 12.45 12.79 0.81 2 4:15 12.92 12.14 12.86 12.76 0.62 3 3:5313.67 13.29 14.15 15.03 1.74 ¹Thickening time test schedule: 80° F. to250° F. and 800 psi to 10,000 psi in 1 hour and conditions held untilcompletion of test. ²Foamed slurry preparation-curing schedule: slurryfoamed with 1000 psi nitrogen pressure, temperature increased from 80°F. to 250° F. (under 1000 psi pressure) in one hour, transferred tocuring cells (at 250° F. and under 1000 psi pressure) and cured in ovenat 318° F.

From the thickening time tests in Table VII, it can be seen that thefoamed cement slurries of this invention will provide the requiredplacement times when a set retarder is included therein. Also, the setfoamed cement slurry settling tests show that very little settling tookplace in the foamed cement slurries of this invention during the timerequired for the foamed cement slurries to set.

Thus, the present invention is well adapted to carry out the objects andattain the ends and advantages mentioned as well as those which areinherent therein. While numerous changes may be made by those skilled inthe art, such changes are encompassed within the spirit of thisinvention as defined by the appended claims.

What is claimed is:
 1. A method of cementing a subterranean zonepenetrated by a well bore comprising the steps of: (a) forming a foamedcement slurry comprised of hydraulic cement, sufficient water to form apumpable slurry, sufficient gas to form a foam and an effective amountof an additive for foaming and stabilizing said slurry comprised ofhydrolyzed keratin; (b) placing said foamed cement slurry into saidsubterranean zone by way of said well bore; and (c) allowing said foamedcement slurry to set into a hard impermeable mass.
 2. The method ofclaim 1 wherein said hydraulic cement is selected from the group ofPortland cements, slag cements, pozzolana cements, gypsum cements, highalumina content cements, silica cements and high alkalinity cements. 3.The method of claim 1 wherein said water is selected from the group offresh water and saltwater.
 4. The method of claim 1 wherein said wateris present in an amount in the range of from about 38% to about 56% byweight of hydraulic cement therein.
 5. The method of claim 1 whereinsaid gas is selected from the group of air and nitrogen.
 6. The methodof claim 1 wherein said gas is present in said foamed cement slurry inan amount in the range of from about 10% to about 40% by volume of saidcement slurry.
 7. The method of claim 1 wherein said hydrolyzed keratinadditive is present in said foamed cement slurry in an amount in therange of from about 1% to about 5% by volume of said water in saidfoamed cement slurry.
 8. A method of cementing a subterranean zonepenetrated by a well bore comprising the steps of: (a) forming a foamedcement slurry comprised of Portland cement, sufficient water to form apumpable cement slurry, a gas selected from the group consisting of airand nitrogen present in an amount in the range of from about 10% toabout 40% by volume of said cement slurry and an additive for foamingsaid cement slurry comprised of hydrolyzed keratin present in an amountin the range of from about 1% to about 5% by volume of water in saidcement slurry; (b) placing said foamed cement slurry into saidsubterranean formation zone by way of said well bore; and (c) allowingsaid foamed cement slurry to set into a hard impermeable mass.
 9. Themethod of claim 8 wherein said water is selected from the groupconsisting of fresh water and saltwater.
 10. The method of claim 9wherein said water is present in said cement slurry in an amount in therange of from about 38% to about 56% by weight of hydraulic cementtherein.
 11. The method of claim 10 wherein said gas is nitrogen.